H.sub.2 --O.sub.2 (air) fuel cells are well known in the art and have been proposed as a power source for many applications. There are several different types of H.sub.2 --O.sub.2 fuel cells including acid-type, alkaline-type, moltencarbonate-type and solid-oxide-type. So-called PEM (proton exchange membrane) fuel cells [a.k.a. SPE (solid polymer electrolyte) fuel cells] are of the acid-type, potentially have high power and low weight, and accordingly are desirable for mobile applications (e.g., electric vehicles). PEM fuel cells are well known in the art, and include a "membrane electrode assembly" (a.k.a. MEA) comprising a thin, proton transmissive, solid polymer membrane-electrolyte having an anode on one of its faces and a cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings therein for distributing the fuel cell's gaseous reactants over the surfaces of the respective anode and cathode catalysts. A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack.
In PEM fuel cells hydrogen is the anode reactant (i.e., fuel) and oxygen is the cathode reactant (i.e., oxidant). The oxygen can either be in a pure form (i.e., O.sub.2), or air (i.e., O.sub.2 admixed with N.sub.2). The solid polymer electrolytes are typically made from ion exchange resins such as perfluoronated sulfonic acid. The anode/cathode typically comprise finely divided catalytic particles (often supported on carbon particles) admixed with proton conductive resin.
For vehicular applications, it is desirable to use a liquid fuel such as a low molecular weight alcohol (e.g., methanol or ethanol), or hydrocarbons (e.g., gasoline) as the fuel for the vehicle owing to the ease of onboard storage of liquid fuels and the existence of a nationwide infrastructure for supplying liquid fuels. However, such fuels must be dissociated to release the hydrogen content thereof for fueling the fuel cell. The dissociation reaction is accomplished heterogeneously within a chemical fuel processor, known as a reformer, that provides thermal energy throughout a catalyst mass and yields a reformate gas comprising primarily hydrogen and carbon dioxide. For example, in the steam methanol reformation process, methanol and water (as steam) are ideally reacted to generate hydrogen and carbon dioxide according to the reaction: EQU CH.sub.3 OH+H.sub.2 O.fwdarw.CO.sub.2 +3H.sub.2
The reforming reaction is an endothermic reaction that requires external heat for the reaction to occur. Heating the reformer with heat generated externally from either a flame combustor or a catalytic combustor is known. The present invention relates to an improved catalytic combustor, and the integration thereof with a fuel cell system, wherein the combustor is fueled with hydrogen-containing anode effluent and oxygen-containing cathode effluent, and includes means at its input end to induce intimate mixing of the anode effluent with the oxygen-dilute cathode effluent to ensure efficient and uniform burning of the hydrogen on the catalyst bed without the creation of "hot spots" or significant temperature differences throughout the catalyst bed.